1. Field of the Invention
The invention generally relates to the improvement of electrical power factor and harmonic power quality at the interface between an electric utility and a utility customer site through the active control of one or more electric appliances at the utility customer's site.
2. Background Information
In the field of electrical power transmission, electrical energy is typically delivered to the electrical consumer as a 60-hz voltage signal. Certain loads, like the inexpensive power rectifier power supplies that are typically supplied with small appliances and computer equipment, pollute the local harmonic content of the electrical supply. Certain applications and facilities such as research facilities and hospitals can be particularly sensitive to the presence of this harmonic pollution. This electrical pollution can decrease the overall distribution grid efficiency and in some cases cause these utilities to over design their distribution and transmission infrastructure. Severe harmonic pollution from one customer's load can affect the performance of and harm a neighboring electrical power customer's loads. Various standards such as IEEE-519 restrict the non-fundamental harmonic components that can be reflected back into the electrical power grid by the electrical loads from these consuming devices. Most electric power customers pay the same for energy consumed by them regardless of its harmonic pollution content.
Harmonic pollution as addressed here includes non-unity power factor electrical currents and those electrical current harmonics above the fundamental 60-Hz AC (alternating current) frequency used in the electrical power distribution system. Reductions in power factor are caused, for example, by rotating induction machines of the type found in clothes washers, dryers, dishwashers, and in refrigeration compressors. Home electronics, computers, and battery chargers and other appliances that possess inexpensive rectifiers, both reduce power factor and create harmonic current pollution at the sites where they reside. The growing abundance of computers and these other appliances in homes and businesses now threatens to become an unchecked, growing source of reduced electric power factor and increased harmonic power quality pollution.
Generally speaking, poor power factor and harmonic pollution from individual residential and commercial appliances can aggregate to become problematic for utilities on distribution feeders. Poor power factor may be mitigated at individual appliances by active power factor correction. Several commercial power factor correction integrated circuits may now be applied to the designs of battery chargers and universal power supplies to force their rectifier stages to consume unity power factor current. Both power factor and harmonic pollution may be corrected at the site-level by expensive power electronic harmonic correctors or, to a lesser degree, by controlled, distributed capacitors. Thus far, such large and active filters have been applied to large commercial and industrial site loads due to their great expense. Unlike active filters and capacitor banks, the present invention does not require the use of electrical energy storage components. Capacitor banks are used at the feeder, substation-level to correct power factor and to reduce harmonic pollution loads, a portion of which would otherwise be passed along through the substation to further aggregate at the transmission levels. However, the utility capacitor bank performs a power factor correction only near the substation where it is located.
The effects of poor feeder-level power factor and harmonic pollution are poor voltage support, energy system inefficiency, and reduction in system component life. In addition, thermal losses in the system reduce overall system efficiency of the distribution system. The additional heat on the lines and transformers can also reduce the usable lifetimes of those power system components and can force de-rating of their capacities during heavy load conditions. What is needed therefore is a system and device that overcomes these problems and provides the desired results.
The present invention provides a cost effective and practical solution to address these issues. Additional advantages and novel features of the present invention will be set forth as follows and will be readily apparent from the descriptions and demonstrations set forth herein. Accordingly, the following descriptions of the present invention should be seen as illustrative of the invention and not as limiting in any way.